Manufacture of organolead compounds



United States Patent MANUFACTURE OF ORGAN OLEAD COL POUNDS Sidney M. Blitzer and Tillmon H. Pearson, Baton Rouge, La., assignors to Ethyl Corporation, New York, N.Y., a corporation of Delaware No Drawing. ApplicationMarch 28, 1955 Serial No. 497,376-

6 Claims. (Cl. 260-437) This invention relates to a process for the. manufacture of organolead compounds. In particular, this invention is directed to an improved process for the manufacture of tetraethyllead.

The process employed in present commercial .practice for the manufacture of tetraethyllead has. been in use for a number of years and, in general, is satisfactory. However, it has certain disadvantages which are overcome by practicing our invention. It proceeds by reacting a sodium-lead alloy, of composition controlled to correspond substantially to NaPb, with ethyl chloride. according to the following equation:

With the highest yields obtained thereby, only about 22 percent of the lead presentin the NaPb alloy is converted to tetraethyllead. Under conditions of best.operation of this process, no one heretofore, as far as we are aware, has been able to increase this yield. of tetraethyllead by even a few percent, due to the inherent limitation in yield as is apparent from the consideration of the above equation. It should be notedthat in this reaction at least 75 percent of the lead originally employed is not alkylated. Thus, in this reaction, large quantities of lead must be recovered and reprocessed to NaPb alloy in order to make it economicaL. A further disadvantage of such a large quantity of unreacted lead is that valuable reaction space in the reactionvessel is occupied by materials which are essentially inert for the manufacture of tetraethyllead under present conditions and mode of operation.

Other processes for the production of organolead compounds, and in particular tetraethyllead,.have been devised to consume the lead produced in the above equation. While such processes are satisfactory from the standpoint of lead consumption, they suffer an additional drawback in common with the present commercial process in that they require organo halide as the ethylating agent. One

such process is that described in U. S. Patent 2,535,190

wherein lead, as for example that produced in the commercial process, is treatedwith metallic magnesium and ethyl chloride in the presence of a catalyst, preferably an alkyl ether. Thus, in this process as well'as the present commercial process, the tetraethyllead manufacturing operation is restricted by the necessary balance between the metallic sodium required and the organic chlorine in the ethyl chloride. i

It is therefore an object of this invention to provide a process for the manufacture of organolead compounds which overcomes the above objections to the present commercial process and those processes which have been proposed more recently as an improvement thereover. Particularly, it is an object of the invention to increase the conversion oflead to tetraethyllead above that obtained in present commercial practice without requiring the use of metallic sodium, metallic lead, or alkyl halogen compound.

These and other objects of this invention are accomplishedby reacting a lead chalkogen, thatis'a'leadoxide or sulfide with an ,organo compound'of the. group IIIA metals containing analkali metal. Thus, the inorganic lead compound is reacted with the lithium, so'diumor potassium aluminum tetraalkyl or*tetraaryl. For convenience, these, compounds are "referred to as tetrahydrocarbo IIIA alkali metals. Inqaccordance with this invention, it has been discovered that to produce organolead compounds it is unnecessary tostart with a lead alloy,.or in fact to employ metalliclead at all. A satisfactory form of the lead to be employed in the process ofthis invention is the common lead ore, galena, or lead sulfide. An additional satisfactory source of'lead for thepresent invention is lead oxide. Similarly,;other oxides .or sulfides of lead can be employed.

The process of the'present invention can best be understood by considering the chemical equation involved. In general, the process proceeds according to the equation and sodium; M is agroup IIIA metal selected from the group'consisting of boron, aluminum, gallium, and indium; and Y is a chalkogen, that is oxygen or sulfur. In the preferred embodiment of this process the organic radicals are alkyl hydrocarbons or'aryl substituted alkyl groups. In'general, we prefer the lower alkyl radicals having up to about'eight carbon atoms. Among the aromatic radicals which can be employed in the above reaction are included phenyl and hydrocarbon substituted phenyl radicals such as the aralkyl radicals. Thus, the compounds AMR may be considered alkylating agents'with respect to the lead in the inorganic leadcompound represented by PbY.

Of greatest current importance from a commercial standpoint is the manufacture of tetraethyllead by the process of this invention. Thisembodiment canbe illustrated by reference to the following equation representing the preferred embodiment.

Illustrative of the alkylating agents which wecan --employ are sodium aluminum tetramethyl, sodium boron tetramethyl, sodium gallium tetramethyl, sodium indium tetraethyl, lithium aluminum tetraethyl, lithium boron tetraethyl, lithium gallium tetraethyl, lithium indium tetraethyl, potassium aluminum tetra (2-phenethyl), potassium boron tetra (2-phenethyl),-potassium galliumtetra (2-phenethyl), potassium indium tetra (Z-phene'thyl), lithium aluminum tetraamyl, lithium boron tetraamyl, lithium gallium tetraamyl, lithium indium tetraamyl, lithiumv aluminum tetraoctyl, lithium boron tetraoctyl, lithium gallium tetraoctyl, lithium indium tetraoctyl, potassium aluminum tetrahexyl, potassium boron tetrahexyl, potassium gallium tetrahexyl, potassium indium tetrahexyl and isomeric derivatives thereof and the like. Likewise, the tetrahydrocarbo IIIA alkali metals can contain a mixture of alkyl radicals and when these are employed, mixed lead alkyls are produced.

By process of this invention, as much as 50 percent of the lead in the foregoing lead salts is directly converted to organo-lead or in particular, in a commercial embodiment, to tetraethyl-lead. The remaining portion of the lead is in a highly active form as lead metal and is ideally suited for employment in the commercial process employing sodium-lead alloy or in that which proposes the reaction of metallic lead with an alkylating agent in the presence of magnesium and a catalyst. Conversely, the lead so produced by thisinvention can be recycled economically to the present process by conversion to the appropriate lead salt. 7

' Our invention is adaptable to the production of organelead compounds generally, such as tetraethyllead, tetramethyllead, dimethyldiethyllead, tetrapr'opyllead, tetra this material is referred to, it is to be understood that other organolead compounds or mixtures can be made by our process. Likewise, sodium aluminum tetraethyl is the preferred alkylating agent and is sometimes referred to hereinafter for specific illustrations. However,

other tetrahydrocarbo HI Ai alkali metals are intended to be inferred therein. a

In general, we contemplate two methods for conducting the process of this invention. One, an alkali metal group III-A hydride is reacted with an appropriate olefin and lead salt to form in one stage the desired organo- 1 lead compound and the by-product alkali metal and aluminum salts and metallic lead. In a second embodiment, in a second stage alkali metal. group I1IA tetrahydrocarbon is reacted with a lead salt, said hydrocarbon compoundhaving previously been prepared by reaction of the alkali metal group IIIA hydride with an appropriate olefin. In both instances, the group III-A hydride is prepared by known methods. For example, lithium aluminum tetra hydride can be prepared by reacting lithium hydride with aluminum chloride and separating the thus produced by-product lithium chloride. For the purposes of this invention, however, it is not essential to remove the lithium chloride as it is essentially inert in the organolead reaction. In the other embodiment, we first 'prepare, for example, lithium aluminum tetraethyl by reaction of lithium aluminum tetra hydride with, ethylene. For the other reactants which are employed in different embodiments of this invention, similar conditionsapply.

Generally, the process ofthis invention is'conducted pressure due to the ethylene increases until reaction commences. Thereupon the ethylene is consumed and the pressure becomes lessened due to the formation of lithium aluminum tetraethyl. Thereupon, this last named compound reacts with the lead salt to produce tetraethyllead. For the preparation in situ of higher alkyl compounds, it is of course not necessary to employ correspondingly high pressures. Thus, with. the normally liquid olefins, a low temperature-low pressure reaction can be em ployed.

While the above operations were discussed in connection with a batch operation, they can be successfully, In addition to applyadapted. to a continuous process. ing the above operations to a continuous process, other modifications of a continuous process can be made, such as first mixing together all the reaction materials and then passing them continuously through a suitable reaction z'one.

It has: been indicated that the process of the present invention is conducted in the presence of an inert carrier liquid. Hydrocarbons of appropriate boiling point with respect to the organolead compound produced are satisfactory and can be chosen so as to provide a solution of the product suitable for other applications or so that as follows. This general description makes references to alkaliv aluminum tetraalkyls but other IIIA compounds are handled similarly. Into a reaction vessel, preferably a' stirred autoclave, is placed the desired quantities of alkali aluminum tetraalkyl compound suspended or dissolved in an inert liquid carrier such as, for example, a. hydrocarbon of medium boiling range. The appropriate lead salt, for example lead oxide in finely divided solid form, is introduced through a hopper containing a plug cock into the autoclave while agitating to create a suspension of the lead salt in the inert liquid carrier. The connection to the hopper is thereupon closed and moderate heat is applied to the reaction vessel While continuing the agitation; Thereupon, an exothermic reaction ensues and upon vreachingthe desired reaction temperature, cooling is provided through a jacket in the autoclave. In contrast to other processes for the manufacture of tetraethyllead, when this invention is em ployed it is not necessary to provide expensive and complex reflux equipment as, by proper choice of the carrier liquid, the reaction can be conducted in a closed system. Thus, tetIaethyllead can be produced without the co-presence of ethyl chloride in the closed vessel. This greatly facilitates control of the reaction and prevents the existence of an otherwise hazardous operation. After completion of the reaction, the organolead compound produced is in solution in the carrier liquid and the other products, namely the alkali metal salt and aluminum salt and metallic lead can be removed by filtration and the organolead compound removed from the carrier by distillation.

Alternatively, an equally satisfactory method ofconducting the process of this invention comprises the formation of the alkylating agent, for example lithium aluminum tetraethyl, in situ in the reaction vessel; Thus,

lithium aluminum-hydride and ethylene and thelead salt are" all introduced to the reaction vessel along with a; liquid carrier. Upon heatingv the reaction,- mixture th they can be readily removed by distillation at a temperature at which the organolead compound will not decompose. Other inert carrier liquids are satisfactory and where the product is a liquid such as, for example, in

the manufacture of tetraethyllead, the organolead'com pound itself can be employed as a carrier liquid. In such an operation, economies are effected by obviating the necessity of recovery by other means than merely filtra-. tion of the co-produced solids.

n'er liquids comprises the liquid amines and liquid ammonia and ethers. The principal criterion of choice therefore, of a carrier, is the physical characteristic .of the organolead compound produced, and the inertn'ess of the liquid to the alkali metal aluminum tetraethyl and the aluminum salt product. Certain'of the aforementioned reactant carriers, while inert to the reactants, exhibit a beneficial effect on the reaction which may be considered'catalyticin nature and contribute to the ease of reaction'and rapidity of arriving at completion of the reaction at relatively lower temperatures and pres sures.

In general, when conducting this process in thepres; ence of a liquid carrier as above, the amount of carrier should be proportioned so as to provide adequate heat removal facilities, In general, the load on the heat transfer medium is proportional to the concentration or relative proportion of the reactants and carrier. In ;a batch operation itis preferred to employ the liquid diluent in the proportion of as much as 1,000 parts per part of organo metallic reactant. In a continuous operation or in an operation providing the maximum heat transfer medium, a more concentrated reaction mixture can .be

employed wherein as little as equal parts by weight of carrier and organo metallic reactant are employed. .In general, it has been found that a more concentrated reac tion mixture provides a rapid reaction and, provided ade quate heat. removal means are provided, this is an ad} vantage as the organolead product is subjected to the.

The reactor was flushed with nitrogen, sealed, andthen pressurized to: 390 pounds per square'inch gage with Another class of car-' a ethylene. It was then heated to a temperature between about 98 and 102 C. and maintained at this temperature for 5 hours. The reactor was then cooled to room temperature, flushed with nitrogen, then 9.56 parts of finely divided lead sulfide was added thereto. The reactor was again sealed and maintained at a temperature between 118 and 122 C. for 4% hours. At the end of this period the reaction mixture was cooled to room temperature and the pressure in the system was released. Sutficient isopropyl alcohol was added to destroy excess lithium aluminum tetraethyl. The reaction mixture was then filtered to remove solids which were recovered for lead value, then the filtrate was washed with an equal volume of water. The organic layer was transferred to a still for the removal by vacuum distillation of the nhexane. The conversion to tetraethyllead recovered was 37.8 percent.

Similarly, when lithium aluminum hydride is reacted with the lead salt in the presence of propylene and butylene, satisfactory yields of tetrapropyllead and tetrabutyllead are produced.

In general, the reaction of this process is completed within a relatively short period at elevated temperatures, but a somewhat longer time is required at lower temperatures. In general, a reaction time of between about onehalf to twenty hours is employed. In particular, in the manufacture of tetraethyllead with lithium aluminum tetraethyl and lead sulfide, we prefer to employ a reaction time of about ten hours or less.

The pressure employed in the reaction vessel is not critical and is usually the autogenous pressure created by the carrier liquid or the olefin ,at the temperature employed. Since organolead compounds are relatively toxic, it is desirable to employ a closed vessel in conducting this reaction which may create an elevated pressure if low boiling carrier liquids are employed.

The temperature required to initiate the self-sustaining reaction of this invention varies with the organolead compound being produced. In general, with the lower alkyllead compounds such as tetraethyllead, it is preferred to employ temperatures in the range of 25 to 150 C. With aryllead compounds, for example tetraphenyllead, it is preferred to operate in the range of 50 to 150 C.

When the reactants in this invention are both solids, and a solvent therefore is not employed, it is preferred in order to provide a relatively rapid and controllable reaction to employ the reactants in finely divided form, or at least in the form of small granules.

While it was indicated above that in general a catalyst is not required for the practice of this invention, certain materials do exhibit a catalytic efiect upon the reaction and, in many instances, their inclusion in the reaction provides a smoother operation. Typical of such mate rials are heavy metal iodides as well as iodine itself,

organic iodides, certain ketones such as acetone and methyl ethyl ketone, and ethers and amines as indicated heretofore.

The following detailed examples serve to illustrate additional specific embodiments of the present invention. However, the invention is not intended to be limited thereto.

Example 11 The procedure of Example I is employed essentially as described with the exception that the lithium aluminum tetraethyl is reacted with 17.9 parts of finely divided lead oxide. Tetraethyllead is obtained in high yield and purity.

In place of the n-hexane employed in the foregoing example as an inert carrier liquid, equally good results are obtained when pentane, benzene, toluene, xylene, triethyl amine, or diphenyl are employed. In addition to the ingredients specified in the foregoing example, thermal stabilizers may be employed, such as, for example, naphthalene and styrene to permit operation of the reaction at still higher temperatures without concomitant decomposition of the tetraethyllead so produced.

Example III Again conducting the process essentially as described in Example I, tetraethyllead is prepared in high purity and yield when reacting another batch of lithium aluminum tetraethyl prepared as described with 18 parts of finely divided lead oxide at a temperature between to C. for a period of six hours.

Example IV When lithium aluminum tetrahexyl is reacted with lead oxide in essentially stoichiometric amounts as described in Example I, tetrahexyllead is produced in high yield.

Example V Lithium aluminum tetra-(Z-phenyl ethyl) is reacted with lead oxide in essentially stoichiometric amounts in accordance with the procedure of Example I to produce tetra-(Z-phenyl ethyl) lead.

We claim:'

1. A process for the manufacture of'alkyllead compounds selected from the group consisting of tetraethyllead through and including tetraoctyllead which comprises reacting a group III-A alkali metal hydride with an olefin corresponding to said alkyl radical and a lead chalkogen wherein the chalkogen is selected from the group consisting of oxygen and sulfur.

2. The process of claim 1 wherein the temperature employed is between about 25 to C. and the reaction is conducted in the presence of an inert liquid carrier.

3. The process of claim 1 wherein the group III-A alkali metal hydride is an aluminum alkali metal hydride.

4. The process of claim 1 wherein the group III-A alkali metal hydride is sodium aluminum hydride, the olefin is ethylene and the lead chalkogen is lead oxide.

5. The process of claim 4 wherein the reaction is conducted at between about 25 to 150 C. in the presence of an inert carrier liquid.

6. A process for the manufacture of tetraethyllead which comprises reacting lithium aluminum hydride with ethylene and lead sulfide.

References Cited in the file of this patent UNITED STATES PATENTS 2,786,860 Ziegler et a1 Mar. 26, 1957 OTHER REFERENCES Leeper et al.: Chem. Revs., 54, 108 (1954), citing Aw tin: I. A. C. S., 54, 3726 (1932). 

1. A PROCESS FOR THE MANUFACTURE OF ALKYLLEAD COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF TETRAETHYLLEAD THROUGH AND INCLUDING TETRAOCTYLLEAD WHICH COMPRISES REACTING A GROUP III-A ALKALI METAL HYDRIDE WITH AN OLEFIN CORRESPONDING TO SAID ALKYL RADICAL AND A LEAD CHALKOGEN WHEREIN THE CHALKOGEN IS SELECTED FROM THE GROUP CONSISTING OF OXYGEN AND SULFUR. 